1. Field of the Invention
This invention relates to flexible polyvinyl chloride plastics having improved flame retardancy and improved smoke suppression properties and to methods of preparing such plastics. In a further aspect this invention relates to a mixture of antimony oxide and a ferrocene derivative.
2. The Prior Art
Two of the major safety problems incident to polyvinyl chloride plastic systems, or other plastic systems, are flammability and smoke generation. Accordingly, many additives and combinations of additives have been added and proposed by the prior art in an attempt to reduce one or the other of these safety problems. Note, for example, U.S. Pat. Nos. 2,894,918; 3,513,119; 3,639,302; 3,676,376 and British Pat. No. 1,049,333. A major problem with these prior art solutions is that typically a system or additive which reduces one of these problems, for instance, i.e. flammability or smoke reduction, inherently causes an increase in the other. Thus, for example, the addition of additives such as antimony oxide (Sb.sub.2 O.sub.3) or tricresyl phosphate to certain plastics produce a dramatic reduction in flammability but cause an increase in the amount of smoke generated by the plastic. Belgium Pat. No. 795,480 discloses that by adding small amounts of ferrocene, or ferrocene derivatives to polyvinyl chloride plastics, that a very substantial reduction in the smoke generating properties of the plastic can be obtained. U.S. Pat. No. 3,926,811 discloses the use of high molecular weight ferrocene derivatives in combination with halogenated paraffins in flexible polyvinyl chloride plastics to improve flame retardancy and reduce smoke generation. A comparison of the % char; oxygen index; and smoke generating properties of a polyvinyl chloride plastic (60% wt. pvc, 40% wt. dioctylphthalate) containing 1% wt. antimony oxide and 0.25% ferrocene with an untreated control sample and samples containing only ferrocene or antimony oxide is shown in Arapahoe Chemicals Data Sheet D2037. The use of ferrocene per se in flexible polyvinyl chloride plastics is impractical since ferrocene diffuses out of the material over prolonged periods of use.
A further difficulty in designing smoke suppressant and/or flame retardant additives for plastics is the empirical nature of the problem, thus until a given additive or combination of additives has actually been used with respect to a given plastic, it is virtually impossible to predict with any certainty what the combined affect on flame retardancy and smoke suppression will be. We have now discovered that by adding small amounts of high molecular weight, ferrocene derivatives and antimony oxide to polyvinyl chloride plastics, and especially flexible polyvinyl chloride plastics, that a substantial increase in smoke reduction and a substantial increase in flame retardancy over the untreated plastic is obtained. This improvement is further generally synergistic with respect to flame retardancy over the summation of the improvement obtained by using the respective additives individually.